This invention relates to audio high fidelity cables or transmission lines wherein the wavelengths of signals carried on the transmission lines are generally longer than the length of the transmission lines, such as in audio signal and high fidelity sound reproduction applications. The invention has particular application where the range of frequencies is greater than several octaves and therefore wherein spurious oscillations (ringing) and broadband random noise carried on the transmission line can have potentially significant impact on the fidelity of a complex signal carried by the transmission line.
In contrast to long transmission lines where the impedance of the cable is matched to the impedance of the termination loads, it is conventional in short transmission lines to reduce the impedance, and more particularly the resistance, of the cable to a minimum to reduce the electrical resistive loss in the cable. When used in high fidelity audio signal interconnection cabling, as between components in an audio component system, such an approach introduces secondary problems, such as audible enhancement of the "brightness" frequencies (1000 Hz to 2000 Hz range) and can cause distortion in the desired audio frequency signals. The primary causes of these effects appear to be radio-frequency noise and spurious oscillation (ringing) in the interconnect cables due to end to end resonances.
It is common practice in audio frequency circuitry to provide either a twisted or parallel pair of signal conductors between subsystems and within components of an audio system. A typical configuration for a current-carrying (1-20 Amperes) loudspeaker connection is a pair of stranded, large gauge (10-16 ga.) wires terminating in a low-impedance (4-16 Ohm) load at the loudspeaker.
Radio frequency noise which is internally generated in audio equipment can be conducted into the signal cable, and can cause spurious oscillations (ringing) and modal resonances in the cable. When the length of the signal lead and the signal return lead are substantially equal, then the natural length-wise mode of ringing in each element is nearly the same, which can result in efficient tuned coupling between the two leads and can cause an increase in the amplitude of the ringing. This is an undesirable condition.
The sources of the radio frequency noise may be either internal (in an amplifier for example) or external (in a television set). The radio frequency noise can cause oscillations and modal resonances in cables and is believed to result in undesired enhancement in the "brightness" frequencies (1000 Hz 2000 Hz range). These effects are undesirable if accurate reproduction of recorded music and the like is desired.
Other cabling schemes are known wherein conductors of slightly different lengths are provided. U.S. Pat. No. 4,538,023 to Brisson illustrates an audio cable wherein conductors of slightly different physical length are provided for the stated purpose of conveying signals of different frequencies having different velocities through appropriate conductors so as to equalize transit times between ends. Brisson has stated that the skin effect is used to this end. Thus, such cables are intended to have the same signal length. By contrast, the present invention relates to a cable wherein the conductors have substantially different signal lengths.
U.S. Pat. No. 4,754,102 to Dzurak discloses a directionally-sensitive audio signal transmission cable which uses multiple conductors which are insulated from one another but which are electrically connected at each end. The uniqueness lies in the fact that less than all of the conductors connected at the source terminal are connected at the destination terminal. The lengths of all conductors are substantially identical. Again by contrast, the present invention relates to a cable wherein the conductors have substantially different signal lengths and all of the conductors connected at the source end are also connected at the destination end.